INTRODUCTION

1.1 BACKGROUND

Coastal evolution since the late Pleistocene had been dominated by repeated changes in

climate, which is well-preserved world over, indicated by penecontemporaneous changes

in sea level. In order to establish local and global variations in sea level during the

Quaternary and to document different episodes of marine transgression and regression,

great deal of work has been carried out in many parts of the world. Worldwide efforts are

also being made to achieve precision in establishing regional sea level curves at site­

specific framework.

1.2 INTERNATIONAL STATUS

For more than a century, earth scientists have been accumulating evidences on sea level

tluctuation during the Quaternary period. The inter-governmental panel on climate change

was in general agreelne,nt on a rise in global sea level in the order of 0.31 to 1.10 01

between 1990 and 2100 (Houghton et aI., 1990). However, a recent estimate suggested a

global mean sea level rise of around 0.2 m during the last century (Pirazzoli, 1986;

Gomitz and Lebedeft, 1987; Douglas and Herbrechsneier, 1989; Peltier and Tushinghorn,

1989~ Klige, 1990; Emery and Aubrey, 1991). Based on the sea level data from different

areas, number of sea level curves has been constructed, which were found to be highly,

useful in reconstructing global scenarios in sea level (Kraft et aI., 1987; Pirazzoli, 1991;~I~ ~'pe:-o~ IPy JP GG ,',.;, OlDOO~

Tushinghom and Peltier, 1993). A~'~ ID '-0--' h:> .~~.# , • uJ ~ ~ .~ i:!:f o·oq 0

+tcZ~~ ~~ ms~ -.I

In 1961, a highly fluctuating sea level curve for the Holocene was established by

Fairbridge and was well referred by the scientific community. During the mid-Holocene,

sea level in some parts of the world was indeed higher than that at present (Dominquez et

aI., 1987; Giresse, 1989). This was in good agreement with most comprehensive

geophysical model of sea level ICE-2 (Peltier, 1988). Much earlier, along the Carolina

coast, Gayes et al. (1992) have reported that a rapid mid-Holocene sea level position,

which was 3 m below the PMSL at 4570-5200 YBP, fell by 1 01 below its position by~'~."'"

4280 YBP. The sea level continued to fall again by 3 m by 3600 YBP, before reaching the

present position. According to Houghton et al. (1990), most of the mid-Holocene

y~~P~~J

warming have taken place prior to 6000A«B~ while most of the higher sea levels

occurred at least 1000 years later. If the same climatic phenomena occur again, with

global warming, the sea-level might register a rise in sea level of the order of few meters

of eustatic sea level rise, instead of few centimeters rise (Kuhn, 1989).

Contrasting effect of tectonic, isostatic and gravitational influences associated with global

variations in ice and water masses rule out the possibility of global applicability of sea

level curves. It is a well-established fact that, changes in shape of the earth's geoid cause

regional differences in the pattern of post-glacial sea level change. In areas such as eastern

South America, West Africa and Australia, sea-level changes are largely caused by

changes in water volume rather than land movement. With the discovery of geoidal

deformation, it becarne obvious that available ocean level changes data base differ widely

over the globe and can never be expressed in terms of globally valid eustatic curves as

previously believed (Fairbridge, 1961; Newman et al., 1980; Bloom, 1983; Momer,

1987b; Pirazzoli, 1991).

For the sake of continuity or discontinuity of forcing functions, it is important to realize

that the earth came into a new lTIode in Mid-Holocene time when the glacial eustatic rise

and corresponding rotational deceleration is finished. The sea level changes became

dominated by redistribution of water masses due to interchange of angular momentum

between the solid earth and main circulation system of the ocean (Morner, 1980; 1995).

With respect to the late Holocene sea-level changes in the order of decades to a century,

there are small to insignificant effects from glacial eustasy due to mass distribution.

Similarly, the effects on the water column are seen only to be in the order of decimeters at

the most (Nakiboglu and Lambeck, 1991; Momer, 1994). The major effects are instead,

the dynamic redistribution of water masses via the ocean current system. It means that

even if the global sea level has changed during the last 150 years, it can only be in the

order of about 1 mm rise per year (Momer, 1992; 1995). During the last of glacial

maximum at about 18,000 YBP, the sea surface circulation pattern.of the Indian Ocean

2

was significantly different from the modem pattern and the SW monsoon wind prevailed

weaker than today (Prell et aI., 1980).

As a result of eustatic rise in sea level, wide assemblages of bivalves and univalve

molluscs got accumulated in the coastal deposits of many p~of the world. They are

considered as well-known geo-scientific tool in deciphering former sea level stands. In

general, the faster the sea level rise, the higher the possibility of its burial, drowning or

destruction. The faster the fall in sea level, the more probable the preservation of

depositional bodies such as beach ridges and coastal dunes. Utilising the interplay

between the inland marine shells and submerged deposits, Fairbridge (1976) was able to

reconstruct various episodes of transgression and regression and was successful in

establishing a sea level curve for that area.

In Europe, North America, Africa and Australia, detailed geomorphological,

palynological, micropaleontological and geoarchaeological studies of the Quaternary

deposits have helped in the reconstruction of different paleogeomorphic environments

(Schumm, 1977; Goudie, 1977; William and Faure, 1980; Butzer, 1980). However, such

studies have clearly demonstrated the complexities involved in the interpretation of

continental sediments and have also helped to highlight the problems encountered in

establishing the cause and effect relationship due to numerous undetectable parameters

involved in the reconstruction of Quatemary Paleogeography.

Seminuik (1981) and Eronen et aI. (1987) utilized the stratigraphic sequences of tidal flats

and swampy environments to deduce past climatic conditions and Holocene sea level

fluctuations. In their pioneering work, Curray and Moore (1964) illustrated the formation

ofbeach ridges and their importance in elucidating sea level changes. Seminuik (1983)

and Tanner (1992, 1993) also emphasized the importance of beach ridge in deciphering

various stages of evolution of the coastal plain.

1.3 NATIONAL STATUS

Studies on the Quaternary deposits along the Indian coasts have received special attention

in the recent years from the point of view of establishing past sea level changes. On the

east coast, sea level studies have mostly been based on depositional and erosional features

exposed in different coastal environments. Available information, however, is more

qualitative. On the contrary, west coast is better investigated by different group of

workers, where, a great deal of information not only on transgressional and regressional

aspects of high strand lines but also on low stands in the continental shelf is available.

In his pioneering work, Ahmed, (1972) correlated disposition of certain land features to

the global inter-glacial transgression/regression. However, during the last two decades,

with the generation of more data, attempts were made to correlate strand line features at

different elevations or depths with that of the glacio-eustatic sea level changes that

occurred during the Quaternary. Analyses of oil-well data from the northern Arabian sea

(Aditya and Sinha, 1976) have found to be highly useful in understanding the sea level

tluctuation during the Tertiary and early Quaternary period.

1.3.1 East Coast

On the east coast, sea level fluctuations were mostly inferred from the studies pertaining

to major river deltas and various coastal landforms like islands, beach ridges, rock

terraces, caves and relict sediments in the continental shelves (Niyogi, 1975; Bhaskara

Rao and Vaidyanathan, 1975; Prudhvi Raju and Vaidyanathan, 1981). Studies on

Holocene sea level changes off Visakhapatnam shelf indicated a late Pleistocene

regression down to about 130 m below thePMSL. Prudhvi Raju et al. (1985) related the

red sand exposures of the Vishakapatnam coast resting over a rock outcrop at about 7 m

above MSL to a high stand of sea level.

Banerjee and Sen (1985) studied the floral and faunal assemblages and informed an

opinion that tidal mangrove forests flourished further north of the. present extent of

4

Sunderbans at about 6000 to 7000 YBP. Niyogi (1971) reported three levels of terrace at

6.1 m, 4.7 m and 3.8 m above MSL in the Subarnarekha River delta and the adjoining

coast of West Bengal.

In the Godavari delta, Sambasiva Rao and Vaidyanathan (1979) grouped four strand lines

under the Holocene period. Samples such as peat/wood material, shell fragments, calcrete

rich mud etc. taken from the farthest beach ridge to the Krishna delta gave an age range of

6500 YBP to 2050 YBP (Krishna Rao et aI., 1990). Radiocarbon dating of mollusc shells

from a bar at about 25 km from the present coastline in the Nizampatnam Bay gave an age

of8200 ± 120 YBP, suggesting a Holocene sea level drop of about 17 m. Here, Srinivasa

Rao et al. (1990) postulated a rapid rise in the sea level at around 8000 YBP, thereby

drowning the barrier island. Evidences of low sea stands at -49 m and -56 m near the

Pulicat Lake in the form of pebble horizons have been identified by Nageswara Rao

(1979).

Meijerink (1971) inferred a low strand line at 70 m, at the close of the Wunn glacial

stage. The sea level rose rapidly to the present level in the course of post-glacial

transgression, thereby inundating 11000-12000 years old Pleistocene fluvial deposits of

the Cauvery region. A series of beach ridges in Cauvery delta, each rising 7.2 m, 6.9 m

and 5.5 m above the PMSL are related to three strand lines at their respective positions

(Sambasiva Rao, 1982).

\'aidyanadhan (1981) related coral reefs and few terraces lying close to Rameswaram

Island between Tamilnadu and Sri Lanka to the emergence of the coast. Morphological

analysis of coastal landfonn indicated emergence of the Rameswaram coast at about 4000

YBP (Rao, 1990). Along the Tamilnadu coast, during the late Quaternary (Upper

Pleistocene) transgression, the sea level rose to +2 m and +8 m during the last inter­

glacial stage. The Holocene transgression reached its maximum height during 6240 YBP

to2740 YBP, the level hardly rising 0.5 m to lrn above the PMSL (Bruckner, 1989). The

terraces around Mandapam and Rameswaram coast ranging in height from 0.20 m to 0.62

5

mabove MSL, gave ages varying from 5440:1: 60 to 140:1: 45 YBP (Victor Rajamanickam

and Lovesan, 1990).

1.3.2 West Coast

In order to establish the tentative Holocene transgression-regression history of the west

coast in chronometric terms, absolute dates of beach rocks, shelf surface sediments,

corals, oolitic limestone etc. from shore and coastal zone have been used by many

workers. Kale and Rajaguru (1983; 1985) inferred a lowering of sea level in the west

coast of India to the tune of 1.5 m to 2.5 m at about 6500 YBP and have also obtained a

sea level curve from the closing phase of Pleistocene to late Holocene. Based on their

work on the Neogene and Quaternary transgressional and regressional history of the west

coast of India, the fluctuation of sea level through time has been attributed to global

eustatic changes in sea level and also to the tectonic movements. From the carbonate

content and the faunal composition of the coastal Arabian Sea sediments, Borole et al.

(1982) provided clear-cut evidences for a major environmental change around 13,000

YBP in the surface ocean waters along the Saurashtra coast.

Based on radiocarbon dates, Agarwal et al. (1973) and Kale et al. (1984) provided

important information on series of transgression and regression phenomenon along the

Maharashtra coast. According to them, before 30,000 to 35,000 YBP, the sea level was

considered to be very much lower than at present, but started rising from 30,000 YBP.

This was followed by a regression, was coupled with a rise in sea level around 15,000

Y"BP. The sea level attained its maximum level during the mid-Holocene. It was also

observed that at about 6000 YBP the sea level was almost the same as that at present, but

insubsequentperiods, i.e. between 6,000 and 2,000 YBP, a further rise of 1 m to 6 m was

indicated. Similarly, Sukhthankar and Pandian (1990) identified various geomorphic

features related to marine regression during Holocene in the Maharashtra coast and

highlighted the significance of neotectonism in shaping the shoreline. Along the Goa

coast, Wagle (1982) inferred presence of drowned river valleys at a depth of 27 m t? 35 m

below the PMSL. Based on oxygen isotope and sedimentological records of a sediment

6

core from the southwestern continental margin of India, fluctuations in sea surface

hydrography during the last deglaciation have been studied by Thampan et al. (2001). The

large glacial-interglacial amplitude in oxygen isotope records and high-amplitude

oscillations within the Holocene suggested influence of deglacial warming and regional

variation in precipitation on the hydrography of the region. Although significant sea

surface warming occurred during the early deglacial period (around 15 ka BP), major

increase in precipitation was only after -9-8 ka BP. The Holocene was also characterised

by large changes in salinity variations and appears to be synchronous with the monsoonal

precipitation events on land.

Extensive studies on the milliolitic rocks of Saurashtra coast resulted in the accumulation

of a wealth of information on high strand line positions during Quaternary (Lele, 1973~

Marathe et aI., 1977; Banerjee and Sen, 1987; Venna and Mathur, 1988~ Purnachandra

Rao and Veerayya, 1996). Synthesizing the observations of different workers, Merh

(1980) illustrated five stages of transgressive and regressive episodes along the Saurashtra

coast. Merh (1992) had also put the highest middle Pleistocene strand line position of the

Saurashtra coast at about 25 m. Thus, it is likely that even 2000 years ago the Rann was

below 4 m of water depth. Studies in the Little Rann also proved to the effect that the sea

level fluctuated even within the Holocene (Gupta, 1975). The existence of an earlier

fluvial network, the role of neo-tectonism and sea level changes are considered to be the

main factors for overall evolution of this part of Western India (Chamayal et aI., 1994).

Studies on the deep sea Arabian Sea cores provide valuable information about the

Quaternary climatic and oceanographic history of this region (Gupta and Srinivasan,

1990a, 1990b; Srinivasan and Singh, 1991, 1992; Singh and Srinivasan, 1993).

Bathymetric and shallow seismic data from the continental slope of Saurashtra-Bombay

indicated presence of wide submarine terraces at 130 m, 145 m and 170 m and reef

structures at 320 m to 360 m water depths.

1.3.2.1 Kerala scenario

In the Kerala coast many studies have been carried out on various aspects of sea level

changes from the point of view of stratigraphic, lithological, geochronological and

7

paleontological framework. (Jacob and Sastri, 1952; Paulose and Narayanaswamy, 1968;

Ramanujam, 1987; Aditya and Sinha, 1976; Raha et aI., 1983, 1987). From the study of

beach rocks along the south west coast of India, Thrivikramji and Ramasarma (1981)

inferred a 4 to 5 m fall in sea level during the Holocene period. Sawarkar (1969) has

located auriferous alluvial gravels farther inland in the Nilambur valley at an elevation of

150 m above mean sea level. Guzder (1980) attributed the alluvial gravels in Nilambur

valley to sea level changes during the early late Pleistocene period. The peat beds that

form prominent Quaternary units in Kerala were considered to be developed from the

submergence of coastal forests, thereby representing series of transgression and regression

(Power et aI., 1983, Rajendran et aI., 1989). The radio carbon dating of decayed wood I.

from carbonaceous clay from Ponnani gave an age of 8230-10240-' YBP indicating

transgression of the sea during Early Holocene period (Rajan et aI., 1992), which

ultimately resulted in destruction of the coastal mangroves.

From the point of view of late Quaternary sea level changes, the continental shelf of

Kerala was explored by many workers. The submerged terraces found at -92 rn, -85 m, ­

75 m and -55 m in the continental shelf of west coast represent four still stands of sea

levels of the Holocene age (9,000-11,000 YBP), the period during which the sea was in a

transgressive phase (Nair, 1974, 1975). Nair and Hashmi (1980) ascribed the formation of

oolitic limestone in the Kerala shelf to warmer conditions and low terrestrial run off

during the Holocene period (9000-11000 YBP). Agarwal (1990) considered the west

coast of India to be an emergent type and identified a rise in sea level to the order of 0.3 m(.

during the past 57 years. I'

\ ...../

Occurrences of typical morphological features along different parts of the Kerala coast do

indicate that there were repeated episodes of transgression and regression (Sarnsuddin et

aI., 1992; Suchindan et aI., 1996; Haneeshkumar et aI., 1998). Sarnsuddin et al. (1992)

considered the strand plain deposits along the northern Kerala coast to be the

morphological manifestations of marine transgression/regressions. The striking

parallelism of Vembanad Lake with that of the series of strand lines in the 'Central Kerala

8

coast is also an example of the transgressive-regressive episodes (Mallik and Suchindan,

1984). A linear sand body at a depth of 20 m to 30 m offshore with typical textural

characteristics of the beach deposits, running almost parallel to this coastline, is also

considered as another example of low stand of sea level (Prithviraj and Prakash, 1991;

Ramachandran, 1992). Relict terrigeneous sediments in the outer shelf between

Mangalore and Cochin imply that the Holocene sedimentation to the outer shelf is

minimal and has been unable to cover the Late Pleistocene sediments. This is confirmed

by the exposure of terrestrial carbonates such as calcretes and paleosols of Pleistocene age"'- ..._-~-~~ ..---

at50 In to 60 m water depth (Rao and Thamban, 1997).

Most of the investigations on the late Quaternary sediments along the Kerala coast were

based either on sequences exposed inland or from the shelf areas. Little attempt has been

made to establish a complete scenario of coastal evolution and climatic changes, which

necessitates a comprehensive study along well-defined E-W transects extending from the

inland across the beach to shelf domain.

1.4 OBJECTI\'ES OF THE STUDY

The northern Kerala coast characterised by series of beach ridges alternating with swales

in the hinterland and occurrence of series of strandline deposits on the shelf offers an

excellent opportunity for attempting a systematic study of coastal evolution and sea level

changes.

In the present investigation, a study was initiated to understand the late Quaternary

fluctuation in sea level and corresponding effect on the shoreline therein with the

following objecti ves:

1. Litho-stratigraphic reconstruction of environments of deposition from the coastal

plain and shelf sequences;

2. Documentation of episodes of transgression and regression by studying different

coastal plain sequences and shelf deposits and

9

3. Evolve a comprehensive picture of late Quaternary coastal evolution and sea level

changes along the northern Kerala coast by collating morphological, lithological and

geochronological evidences from the coastal plain and shelf sequenc·es.

1.5 PHYSIOGRAPHY

Physiographically, the State can be classified into five zones (Resource Atlas of Kerala,

1984). The mountains and peaks that rise above 1800 m within the Western Ghats

constitute only 0.64% of the total area. The highlands at an altitude of >75 m occupy

20.35°A> of the area.

The undulating western fringe of the highlands and lateritised rocky spurs projecting

westward fonn the midlands within altitude of 8 m to 75 m cover nearly 8.44% of the

total area. The areas falling below the altitudinal range of <8 m, and which consists of

dissected peneplains constitute the lowlands. Numerous flood plains, terraces, valley hills,

colluvium and sedimentary formation are parts of these landfonns. In the northern and

southern parts of the State this unit merges with the coastal plain.

Coastal plains, with lagoons and vast low-lying areas fringing the coast, is not only an

important physiographic unit of Kerala, but also important in terms of economic activity

and demographic distribution. In this physiographic zone, most of the areas show relief

between 4 ID to about 6 m above MSL. Beach dunes, ancient beach ridges, barrier flats,

coastal alluvial plains, flood plains, river terraces, marshes and lagoons constitute this

unit. A characteristic feature of this unit is the series of beach ridges and swales roughly

aligned parallel to the coast.

1.6 GEOLOGY OF KERALA

Four major lithologic units are reported from the northern Kerala coast (Fig 1.1). viz.,

Precambrian Crystallines, Tertiary Sedimentaries, Laterite cappings over Precambrian

Crystallines, and the Recent to Sub-Recent sediments.

10

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Precambrian Crystallines: The Precambrian crystallines, which include Charnockite group,

Migmatite complex, Khondalite group, Wyanad group, Peninsular gneissic complex,

Dharwar super group and some basic and acidic rocks (GSI, 1995), occupy considerable

portions of northern Kerala. The former three cover more than 80% of the total area of

Kerala.

Tertiary Sedimentaries: The Tertiary sedimentary formation of Kerala unconfonnably lie

over the Precambrians. It is the southern-most one among the chain of Tertiary basins

along the west coast of Peninsular India. Inland part of the Tertiary basin consists of

Neogene and Quaternary sediments. Neogene sediments comprise a series of variegated

sandstones and clays with lenticular seams of lignite (Warkalli beds) and more compact

sands and clays with thin beds of limestone named as Quilon beds (Paulose and

Narayanaswamy, 1968).

Quater"ary Sediments: The Quaternary sediments include parallel sand ridges, sand flats,

alluvial sands and lacustrine deposits. The coastal plain, generally do not rise more than

15 m above MSL. The coastal sands at places are rich in heavy minerals such as ilmenite,

monazite, zircon, rutile etc.

1.7 CONTINENTAL SHELF AND BATHYMETRY

The continental shelf bordering the west coast of India is remarkably straight, which is- ~

considered to be formed due to faulting during the Pleistocene (Krishnan, 1968). The

shelfalong this part is broader and flatter when compared to world averages. Width of the

shelfincreases from 40 km off Trivandrum in the south to 320 km off the Gulf ofCambay

in the north (Ramaraju, 1973). Based on the surface roughness of the continental shelf,

Siddique and Raj amanickam (1974) ascribed the shelf break between 120 m and 145 m

and the average shelf break occurring at a water depth of 100 m. Topographic studies on

the outer shelf of the western continental shelf indicated small scale irregularities of the

order of 1-8 m in height at depth between 35 m and 145 m. (Nair, 1975; Wagle. et aI.,

12

1994; Subbaraju and Wagle, 1996). Generally the shelf has a gentler slope near the sh

and the gradient increasing further seawards.

1.8 CLIMATE

Kerala State has a tropical humid climate with an oppressive summer and plentiful

seasonal rainfall. The hot summer season from March to May is followed by SW

monsoon from June to September. October andNovember months form the post monsoon 1~_. __.. '-..._-.- '. '. -'_.•..._.._._,-._... -_...... -.., ..

or the retreating monsoon season. The period from October to December is the N-E \.- -- ---' -- ~ -- . ~

monsoon season (Resource Atlas of Kerala). It is because of the seasonal reversal of wind ;

circulation in the Arabian Sea, the monsoonal climate is generated along the SW coast of

India. The climate of Kerala is broadly grouped under the following season

(Ananthakrishna et aI., 1979): viz., winter month (January-February), hot weather period

(March-May), SW monsoon (June-September) and NE monsoon (October-November).

1.9 \VA VE CLIMATE

Though there are seasonal variations In the occurrence of wave activity, generally

maximum wave activity is observed during the monsoon months, During the fair season,

the wave height is less than 1m. Increase in wave activity is evident in the monsoon

months, Wave height during the rough season is more or less normally distributed. The

maximum breaker height generally shows a peak during June-July, while it is low from

October through March. The increase in breaker height commences in May and continues

till September. The distribution of mean monthly breaker period generally shows that

waves break at higher frequency during the S- W monsoon. The longshore currents also

vary considerably in time and space. The currents are towards south during the monsoon

period. During the non-monsoon months, it shifts towards north. However, there are

exceptions to these general trends. During the monsoon months there are both alongshore

and onshore-offshore component of current. Under the influence of the longshore and

onshore-offshore currents, the beaches erode to a great extent during the monsoon. Non­

monsoon months are characterised by constructive wave action, thus accelerating building

up ofbeach to a great extent.

13

1.10 FLUVIAL INPUTS

Out of the 44 rivers that drain the State of Kerala, 3 are east flowing. Absence of delta

formation is the characteristic feature of the Kerala Rivers. Most of the river courses are

straight, indicating a structural control. Major rivers that drain the study area are:

Karingote, Nileswaram, and Valapatnam. Drainage basins of these rivers are occupied by

chamockite, khondalite, different type of gneisses, sediments of Tertiary age, laterite

cappings on crystallines and sediments of Sub-Recent to Recent age. The characteristic

features of the rivers are given in Table 1.1

Table 1.1 Length of rivers (km), their catchment area (krrr') and total run off(1000Mc ft).

SI. no River Length Catchment area Run-off

1 Karingote river 64 561 50.36

2 Ni1eswaram river 46 190 16.5

3 Va1apattanam river 110 867 97.7

1.11 STUDY AREA

The region of investigation lies in the coastal plain of the northern Kerala coast in the

Kasaragod district. To understand the coastal evolution with all the aspects of sea level

changes during the Pleistocene to Holocene period, a systematic study along two shore­

nonnal East-West transects originating from the strand plain and cutting across the beach

to the shelf domain is attempted. The study was carried out along Punjavi­

Muthappankavu (Latitude 12° 17' 30" and Longitude 75° 5' to 75° 7' 30') and Padanna­

Onakkunnu (Latitude 12° 10' and Longitude 75° 7' 30" to 75° 10') regions of the northern

Kerala coast. Location map of the study area is illustrated in Figure 1.2. The coastal plain

sequence of Punjavi transect, with a landward extension of about 2.4 km is further

extended to 78 km towards the continental shelf. The Onakkunnu transect that l1as about

6.4 km landward length is extended to about 74 km into the continental shelf. Detailed

location map of the study area showing core locations are given in the corresponding

Chapters.

14

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